KR20180127970A - Separator and Secondary Battery for Secondary Battery - Google Patents

Abstract

An object of the present invention is to provide a separator for a secondary battery which is low in cost and exhibits adhesion with an electrode and dimensional stability. The present invention relates to a separator in which a porous substrate is laminated with at least one surface of an inorganic particle and a porous layer composed mainly of two or more kinds of organic resins having different melting points on at least one surface thereof, And / or (B). (A) the porous layer has a melting point of 130 ° C or more and 20 ° C or more and less than 130 ° C. (B) The porous layer has a melting point of 130 ° C or more and has an amorphous organic resin

Description

Separator and Secondary Battery for Secondary Battery

The present invention relates to a separator for a secondary battery and a secondary battery.

Secondary batteries such as lithium ion batteries are widely used in portable digital devices such as mobile phones, notebook computers, digital cameras, digital video cameras, and portable game machines. 2. Description of the Related Art [0002] In recent years, the use of automobiles as power sources for hybrid cars, electric vehicles, plug-in hybrid cars and the like has been expanded.

A lithium ion battery generally has a structure in which a separator for a secondary battery and an electrolyte are interposed between a positive electrode in which a positive electrode active material is laminated on a positive electrode collector and a negative electrode in which a negative electrode active material is laminated on a negative electrode collector.

As a separator for a secondary battery, a polyolefin porous substrate is used. As the characteristics required for the separator for a secondary battery, there are a property of containing an electrolyte in the porous structure and allowing ion movement, and a phenomenon that when the lithium ion battery is abnormally heated, the porous structure is closed by melting with heat, And stopping the power generation by stopping the power generation.

However, in order to prevent a gap from being generated between the electrode and the secondary battery separator by repeating charge and discharge as well as the above characteristics in accordance with the recent increase in the capacity and output of the lithium ion battery, deterioration of cycle characteristics is caused in the secondary battery separator, (Wet adhesiveness) with the electrode in the impregnated state is required. In addition, with the recent increase in the capacity and output of lithium ion batteries, high safety is demanded for the secondary battery separator. In addition, in order to prevent a short circuit due to contact between the positive electrode and the negative electrode, which is caused by heat shrinkage of the separator for the secondary battery at high temperature, the secondary battery separator is required to have dimensional stability. In order to maintain the shape of the laminate when the laminate in which the positive electrode, the separator, and the negative electrode laminated is transported in the production process of the secondary battery, or the laminated product of the wound positive electrode, the separator and the negative electrode may be formed into a cylindrical shape, The separator for a secondary battery is required to have adhesiveness (dry adhesiveness) between the separator and the electrode before impregnating the electrolyte, so that the form of the laminate does not collapse when pressed before being inserted into the die. In addition, with the spread of the secondary battery, it is required to lower the manufacturing cost of the secondary battery, and the cost of the secondary battery separator is required to be reduced.

With respect to these requirements, in Patent Documents 1 and 2, a separator for a secondary battery improved in wet adhesion with an electrode by laminating a porous layer composed mainly of a polyvinylidene fluoride resin having wet adhesion property on a porous substrate made of polyolefin Has been proposed. Patent Document 3 proposes a separator for a secondary battery in which wet adhesion with an electrode is improved by laminating a porous layer composed mainly of particles of polyvinylidene fluoride resin having wet adhesion property on a porous substrate made of polyolefin . Patent Document 4 discloses a separator for a secondary battery having improved wet adhesion and dimensional stability to an electrode by laminating a porous layer made of a polyvinylidene resin having adhesive properties and a porous layer made of inorganic particles onto a porous substrate made of polyolefin Has been proposed.

Japanese Patent Application Laid-Open No. 2004-146190 Japanese Patent Application Laid-Open No. H02-221741 Japanese Patent No. 5355823 International Publication No. 2013/133074 pamphlet

However, in Patent Documents 1 and 2, it has been proposed to form a porous layer by coating a release film or a porous substrate with a fluororesin dissolved in an organic solvent and immersing it in a coagulation bath. However, The wet adhesion with the electrode of the separator for a secondary battery is improved, but the production cost is high and it is not possible to meet the demand for lowering the current cost for the secondary battery separator. Further, the dry adhesiveness with the electrode in a state in which the electrolyte solution is not impregnated is not sufficient. In Patent Documents 3 and 4, since the molecular weight of the polyvinylidene fluoride resin to be used is not appropriate, wet adhesion with a sufficient electrode can not be obtained. Further, the dry adhesiveness with the electrode in a state in which the electrolyte solution is not impregnated is not sufficient.

Accordingly, an object of the present invention is to provide a secondary battery separator that exhibits wet adhesion, dry adhesiveness, and dimensional stability to an electrode at low cost in view of the above problems.

Therefore, the inventors of the present invention have conducted intensive investigations in order to exhibit wet adhesion, dry adhesiveness, and dimensional stability to electrodes in a separator for a secondary battery at low cost. As a result, it has been found that when the fluororesin and the organic resin having a specific range of melting point are used, the wet adhesion and the dry adhesion with the electrode are manifested. Further, by coating the coating material mixed with the inorganic particles by the general application method by the granulation of the fluororesin, the wet adhesion with the electrode, the dry adhesiveness, and the dimensional stability can be manifested at low cost.

In order to solve the above problems, the separator for a secondary battery of the present invention has the following configuration.

(1) A separator obtained by laminating at least one surface of a porous substrate with a porous layer containing inorganic particles and at least two kinds of organic resins having different melting points as a main component, wherein at least one of the organic resins is a fluororesin, / (B).

(A) the porous layer has a melting point of 130 ° C or more and 20 ° C or more and less than 130 ° C

(B) the porous layer has a melting point of 130 ° C or higher and has an amorphous organic resin

(2) A separator in which at least one surface of the organic resin is a fluororesin, and the porous layer has a thickness of not less than 130 DEG C And a melting point of from 20 캜 to less than 130 캜.

(3) The separator for a secondary battery according to (1) or (2), which satisfies the following (C) and / or (D)

(C) the porous layer has a melting point of 130 占 폚 or more and less than 180 占 폚 and 20 占 폚 or more and less than 130 占 폚

(D) the porous layer has a melting point of 130 ° C or more and less than 180 ° C, and has an amorphous organic resin

(4) The separator for a secondary battery according to any one of (1) to (3), wherein the organic resin comprises an acrylic resin and / or an olefin resin.

(5) The separator for a secondary battery according to any one of (1) to (4), wherein at least one of the organic resins has an acidic functional group.

(6) The separator for a secondary battery according to any one of (1) to (5), wherein the fluororesin is a polyvinylidene fluoride resin having a vinylidene fluoride content of 80 mol% or more and 100 mol% or less.

(7) The separator for a secondary battery according to (6), wherein the polyvinylidene fluoride resin has a melting point of 130 ° C or higher.

(8) The separator for a secondary battery according to (6) or (7), wherein the polyvinylidene fluoride resin is in the form of particles and has an average particle diameter of at least 0.01 탆 and less than 1.00 탆.

(9) A secondary battery using the separator for a secondary battery according to any one of (1) to (8).

(Effects of the Invention)

According to the present invention, by satisfying the following (A) and / or (B), the porous layer has two or more kinds of organic resins having different melting points as main components and at least one kind of fluorine resin, Adhesion can be imparted, and dimensional stability can be imparted by containing inorganic particles in the porous layer.

(A) the porous layer has a melting point of 130 ° C or more and 20 ° C or more and less than 130 ° C

(B) the porous layer has a melting point of 130 ° C or higher and has an amorphous organic resin

By using the separator for a secondary battery of the present invention, it becomes possible to provide a secondary battery such as a high-capacity, high-output, long-life, low-cost lithium ion battery.

A separator for a secondary battery according to the present invention is a separator in which a porous layer composed mainly of inorganic particles and two or more kinds of organic resins having different melting points is laminated on at least one surface of a porous substrate, (A) and / or (B) of the separator.

(A) the porous layer has a melting point of 130 ° C or more and 20 ° C or more and less than 130 ° C

(B) the porous layer has a melting point of 130 ° C or higher and has an amorphous organic resin

Hereinafter, the present invention will be described in detail.

[Porous layer]

(Organic resin)

The porous layer of the present invention is composed mainly of two or more organic resins having different melting points from the inorganic particles. At least one kind of organic resin is a fluororesin. Here, the melting point refers to the peak top of the endothermic peak at the time of the first temperature rise and the second time of the temperature rise in the differential scanning calorimetry (DSC) according to " JIS K7121: Hereinafter sometimes referred to as " peak top "). Also, the melting point is different not only when the organic resin of each other has a melting point and the melting point is different but also when one organic resin has a melting point and the other organic resin is an amorphous organic resin.

As the organic resin constituting the porous layer of the present invention, an organic resin such as an olefin resin such as polyethylene and polypropylene, an acrylic resin, a styrene-butadiene resin, a crosslinked polystyrene, a methyl methacrylate- styrene copolymer, a polyimide, Melamine resin, phenol resin, polyacrylonitrile, silicone resin, urethane resin, polycarbonate, carboxymethylcellulose resin and the like. The term " main component " means that the ratio of the inorganic particles to the total of the porous layers of two or more types of organic resins having different melting points is 70% by mass or more.

Of these resins, two or more kinds of fluororesins having different melting points may be used. One or more kinds of organic resins other than the fluororesin and fluororesin having different melting points from the fluororesin may be used. Two or more kinds of organic resins having different melting points from the fluororesin may be used. In particular, as the other organic resin having a melting point different from that of the fluororesin, it is preferable to use an acrylic resin and / or an olefin resin in terms of electrical stability and oxidation resistance.

One form of the porous layer of the present invention has a melting point of 130 占 폚 or more and 20 占 폚 or more and less than 130 占 폚. That is, the porous layer of the present invention has at least one melting point at 130 ° C or higher and at 20 ° C or higher and lower than 130 ° C, respectively, when the melting point of the porous layer is measured by the method described in the embodiment. 130 占 폚 or higher, and 20 占 폚 or higher and 130 占 폚 or less, respectively. One at 130 ° C or higher and two or more melting points at 20 ° C or higher and lower than 130 ° C or two or more melting points at 130 ° C or higher and one melting point at 20 ° C or higher and lower than 130 ° C, And at least two melting points at 20 ° C or more and 130 ° C or less at the same time.

The porous layer of the present invention preferably has a melting point of 130 ° C or more and less than 180 ° C and 30 ° C or more and less than 120 ° C. More preferably 140 占 폚 or more and less than 180 占 폚, and more preferably 40 占 폚 or more and less than 100 占 폚.

An organic resin having a melting point of 130 ° C or higher and an organic resin having a melting point of 20 ° C or higher and lower than 130 ° C are preferably used in the porous layer of the present invention. More preferably, an organic resin having a melting point of 130 ° C or more and less than 180 ° C or an organic resin having a melting point of 30 ° C or more and less than 120 ° C is used. More preferably, an organic resin having a melting point of 140 ° C or higher and lower than 180 ° C or an organic resin having a melting point of 40 ° C or higher and lower than 100 ° C is used. An organic resin having a melting point of 130 ° C or higher is used as an example to obtain wet adhesion with an electrode. When the melting point is lower than 130 占 폚, sufficient wet adhesion may not be obtained. An organic resin having a melting point of 20 占 폚 or more and less than 130 占 폚 is used as an example to obtain dry adhesion with an electrode. When the melting point is lower than 20 占 폚, there is a case where battery characteristics are deteriorated by deformation when the secondary battery is repeatedly charged and discharged and by elution into the electrolyte solution. When the melting point is 130 占 폚 or higher, dry adhesion with an electrode may not be obtained sufficiently.

One form of the porous layer of the present invention has a melting point of 130 DEG C or higher and also has an amorphous organic resin. The amorphous organic resin referred to herein refers to a resin that does not have a melting point, that is, does not have an endothermic peak in the measurement by a differential scanning calorimeter. That is, the porous layer of the present invention has at least one melting point at 130 占 폚 or higher when the melting point of the porous layer is measured by the method described in the embodiment. Or may have two or more melting points at 130 ° C or higher. The porous layer of the present invention preferably has a melting point of 130 ° C or more and less than 180 ° C, and more preferably a melting point of 140 ° C or more and less than 180 ° C.

It is preferable that at least one of the organic resins has an acidic functional group in order to improve wet adhesion with the electrode. In the case of having an acidic functional group, it is also possible to improve the productivity and the battery characteristics in the production of the secondary battery by improving the affinity with the electrolytic solution. Acidic functional groups are functional groups capable of releasing protons (H ⁺ ). Specific examples of the acidic functional group include a carboxylic acid group, a sulfonic acid group, a phosphoric acid group, a hydroxyl group, and a phenolic hydroxyl group. One kind may be used, or two or more kinds may be used.

Examples of the monomer having a carboxylic acid group include monocarboxylic acids and derivatives thereof such as acrylic acid, methacrylic acid and crotonic acid, and derivatives thereof such as maleic acid, fumaric acid, itaconic acid, Dicarboxylic acids such as lacconate, and acid anhydrides thereof, or derivatives thereof. These may be used alone or in combination of two or more. Among them, dicarboxylic acid is preferable, and maleic acid is particularly preferable.

The shape of the organic resin may be either a particle shape or a particle shape. Examples of the shape of the particles include spherical, plate, needle, bar, and oval shapes, and any shape may be used. Among them, spherical shapes are preferable from the viewpoint of surface water repellency, dispersibility, and applicability. In the state of the coating liquid prior to the formation of the porous layer, the coating liquid may be in the form of a particle and may be formed into a film without forming a particle shape by heat at the time of formation. Alternatively, a film may be partially formed so that adjacent particles are connected to each other through a film.

(Fluororesin)

Examples of the fluororesin constituting the porous layer of the present invention include homopolymers such as polyvinylidene fluoride, polytetrafluoroethylene, polyvinyl fluoride and polychlorotrifluoroethylene, ethylene-tetrafluoroethylene polymers, ethylene-chlorotri And copolymers such as fluoroethylene polymers. Further, homopolymers and copolymers such as tetrafluoroethylene, hexafluoropropylene, trifluoroethylene and the like can be mentioned. Among these fluororesin resins, polyvinylidene fluoride resins, in particular, resins composed of a copolymer of vinylidene fluoride and hexafluoropropylene are suitably used in terms of electrical stability and oxidation resistance.

The vinylidene fluoride content of the polyvinylidene fluoride resin is preferably 80 mol% or more and 100 mol% or less. More preferably, it is 85 mol% or more and 99 mol% or less. More preferably, it is 90 mol% or more and 98 mol% or less. If the vinylidene fluoride content is less than 80 mol%, sufficient mechanical strength may not be obtained.

It is preferable that the polyvinylidene fluoride resin has a melting point of 130 캜 or higher. More preferably, the melting point is not less than 130 ° C and less than 180 ° C, and more preferably not less than 140 ° C and less than 180 ° C.

The weight average molecular weight of the fluororesin is preferably 100,000 or more and 5,000,000 or less. More preferably not less than 300,000 and not more than 4,000,000. More preferably not less than 600,000, and further not more than 3,000,000. Particularly preferably not less than 800,000 and not more than 2.5 million. When the weight average molecular weight is less than 100,000, adhesion with the electrode may not be obtained sufficiently. When it is greater than 5,000,000, handling and coating properties may be lowered due to viscosity increase.

The fluororesin of the present invention may be mixed with a plurality of types of fluororesin. When a plurality of kinds of fluororesins are mixed, it is preferable that a plurality of kinds of fluororesins are combined to have a weight average molecular weight of 100,000 or more and 5,000,000 or less. However, for example, when the shell is the fluororesin of the present invention and the core is a separate fluororesin, the weight average molecular weight of the fluororesin may not be 100,000 or more and 5,000,000 or less.

The fluororesin may be in the form of particles, and the average particle diameter is preferably 0.01 탆 or more and 1.00 탆 or less. More preferably not less than 0.02 占 퐉, and not more than 0.40 占 퐉. More preferably not less than 0.04 占 퐉, and not more than 0.20 占 퐉. When the average particle diameter is smaller than 0.01 탆, the fluororesin particles are densely laminated, and the increase in air permeability may be increased. When the average particle diameter is larger than 1.00 mu m, the contact area with the electrode becomes small, and sufficient wet adhesion may not be obtained. In addition, since the distance between the inorganic particles is increased, the dimensional stability may be lowered.

The average particle diameter in this case is measured by measuring the length of a long side (long axis diameter) of one side of a square or a rectangle in which the fluorine resin particles observed by microscopic observation of the surface of the porous layer are completely surrounded , And the number average is calculated. Details of the measurement method will be described later.

Examples of the shape of the fluororesin particles include a spherical shape, a plate shape, a needle shape, a bar shape, an oval shape and the like, and any shape may be used. Among them, a spherical shape and a plate shape are particularly preferable from the viewpoints of dispersibility, coatability and porosity.

The aspect ratio of the fluororesin particles is preferably 100 or less, more preferably 50 or less, and further preferably 30 or less. When the aspect ratio is larger than 100, the handling property of the fluororesin particles may be lowered.

Here, as described in the embodiment, the aspect ratio refers to the ratio of the length of the long side (long axis diameter) of the rectangular shape divided by the short side (short axis diameter) to the square or rectangular shape in which the particles are completely surrounded on the image of the particles obtained by the electron microscope Value. In the case of a square, the aspect ratio is 1.

As the method for producing the fluororesin particles, known production methods such as emulsion polymerization, suspension polymerization and dispersion polymerization can be used. Further, the fluororesin particles obtained by the above-mentioned production method may be further processed to obtain the target average particle diameter and shape. For example, a solidification method, a phase separation method, a dry milling method, a wet milling method, a spray dryer method and the like.

Examples of the coagulation method include a method of dissolving a fluororesin in a solvent or a solvent and water, and adding a fluororesin solution to a poor solvent to precipitate the fluororesin particles.

For example, the solvent used to dissolve the fluororesin is a solvent that dissolves the fluororesin, and may be any solvent that can be mixed with water.

Specific examples of the solvent include N-alkylpyrrolidone solvents such as N-methyl-2-pyrrolidone (hereinafter also abbreviated as NMP), 1,3-dimethyl-2-imidazolidinone (Hereinafter may be abbreviated as DMF), such as urea-based solvents such as N, N-dimethylacetamide (hereinafter sometimes abbreviated as DMAc) and N, N-dimethylformamide Sulfuric acid polar solvents such as dimethylsulfoxide, dimethylsulfone and tetramethylene sulfone; ketone solvents such as acetone and methyl ethyl ketone; nitriles such as acetonitrile and propionitrile; Based solvent. Among them, NMP, DMI, acetone, methyl ethyl ketone and acetonitrile are preferable, and NMP and acetonitrile are more preferable for stability of the solvent and ease of industrial handling.

Since the atmosphere of the melting tank suppresses decomposition and deterioration of the fluororesin, it is preferable to lower the oxygen gas concentration. Therefore, it is preferable to dispose the dissolution tank under an inert gas atmosphere. Examples of the inert gas include nitrogen gas, carbon dioxide gas, helium gas, and argon gas. Nitrogen gas, argon gas and carbon dioxide gas are preferable in view of economical efficiency and availability. Particularly preferably, nitrogen gas or argon gas is used.

The dissolving method is not particularly limited, but when a fluororesin solution is prepared, a fluororesin, a solvent and water are put into a predetermined container and dissolved with stirring. If it is not dissolved at room temperature, it is dissolved by heating.

After the fluororesin is dissolved in a solvent, water may be added. In the method of adding water after dissolution, a fluororesin solution is prepared in a predetermined vessel, and then water is added to the fluororesin solution. For the addition of water, a liquid delivery pump, a Komagome pipette or the like can be used. If a large amount of water is added at once, fluororesin precipitates and it takes a long time to dissolve the fluororesin. Therefore, it is preferable to gradually add water. In order to produce fluororesin particles having uniform particle diameters, it is preferable to completely dissolve the fluororesin in a solvent and then add it to a poor solvent, or precipitate by flash crystallization. There may be a fluorine resin of an unexposed solution.

The amount of water to be added varies depending on the concentration of the fluorine resin to be dissolved and the type of the solvent. The amount of water to be added is preferably 1% by mass or more and 25% by mass or less in the total amount of 100% by mass of the solvent and water to be added. If the amount of water to be added is excessively small, there are cases where the release particles are formed, and if the amount of water to be added is excessively large, the fluororesin may be precipitated.

The dissolution temperature depends on the type of solvent used and the concentration of fluorine resin. But is usually from room temperature to 200 ° C, preferably from room temperature to 100 ° C, or the boiling point of the solvent.

The dissolution time varies depending on the type of solvent, the concentration of the fluororesin, and the dissolution temperature. Is usually in the range of 5 minutes to 50 hours, preferably in the range of 10 minutes to 40 hours.

If the concentration of the fluororesin is high, the fluororesin solution may be fused to the poor solvent when the fluororesin particles are precipitated. Therefore, fluororesin particles having small particle diameters or fluororesin particles having uniform particle diameters may not be obtained.

Therefore, the amount of the fluororesin in the fluororesin solution is 100% by mass when the fluororesin solution contains no water, 0.1% by mass or more and 15% by mass or less with respect to the total amount of 100% by mass of the solvent and water, . And more preferably 0.5% by mass or more and 10% by mass or less.

The poor solvent will be described later in detail.

When the total amount of the solvent and water is 100% by mass, the fluororesin content is preferably 0.1% by mass or more and 15% by mass or less, because the possibility of application to industrial production is improved. In the present embodiment, the fluororesin solution is provided in the precipitation step after the fluororesin is dissolved in the solvent or the solvent and water.

Examples of the precipitation step include the following (step a1), particularly (step a2).

(a1 step) A step of precipitating fluorine resin particles by adding a fluorine resin solution to a poor solvent

(a2 step) A step of flash-crystallizing a fluorine resin solution into a poor solvent to precipitate fluorine resin particles

(a1 step), a fluororesin solution is added to a poor solvent of the fluororesin to precipitate the fluororesin particles. In the case of adding the fluororesin solution to the poor solvent of the fluororesin, the solution may be continuously injected into a container containing a poor solvent of the fluororesin (hereinafter sometimes referred to as " receiving tank ") from a container containing the fluororesin solution, good. Further, the fluororesin solution may be added via the vapor phase from above the poor solvent. It is preferable to be directly put into a poor solvent in view of obtaining fine particles having uniform particle diameters.

A method of preparing a fluororesin particle by contacting a fluororesin with a poor solvent includes a method in which a fluororesin solution is added to a water holding vessel containing a poor solvent to prepare a particle solution and then the particle solution is withdrawn and provided in the next step (Batch) and continuous flow (sometimes simply abbreviated as continuous). The reactor used in the continuous flow type is a continuous stirred tank reactor (abbreviation: CSTR) and a plug flow reactor (abbreviation: PFR). Any reactor can be adapted to the granulation of the fluororesin.

In the method of using CSTR, a poor solvent is put in a receiving tank (which may be referred to as a reactor in a continuous system), a fluororesin solution is added to prepare fluororesin particles, and then a fluororesin solution And a poor solvent are simultaneously dripped, and the granulating liquid of the fluororesin is continuously drawn out from the receiving tank and continuously granulated. It is also possible to prepare a granulated liquid by sequentially drawing the fluorinated resin granulated liquid from the receiving tank while simultaneously dropping the fluorinated resin solution and the poor solvent into the granulated liquid of the fluorinated resin produced by the batch method.

When CSTR is used, it is preferable to drop the fluororesin solution and the poor solvent at the same time. The dropping rate ratio of the poor solvent to the dropping rate of the fluororesin solution is not particularly limited as long as the fluororesin particles can be produced. From the viewpoint of the productivity, the dropping rate ratio of the poor solvent to the dropping rate of the fluororesin solution is 0.1 to 100 , More preferably 0.2 to 50%.

The ratio of the mass of the granulated liquid in the receiving tank to the flow rate of the granulated liquid from the receiving tank (reactor) is defined as the residence time. The retention time is not particularly limited as long as fine particles having uniform particle size can be obtained, and is preferably 1 second to 10 hours, more preferably 1 minute to 1 hour.

A mixing device may be provided in the holding tank to maintain the uniformity of the granulating liquid. Examples of the mixing apparatus include a stirring blade, a twin-screw mixer, a homogenizer, and an ultrasonic irradiation.

The method of using PFR is a method in which a fluororesin solution and a poor solvent are passed through a pipe at a constant rate to mix a fluororesin solution and a poor solvent in a pipe to carry out the granulation and continuously take out the granulated liquid, Can be used. For example, when two pipes are used, the fluorine resin solution may be passed through the inner tube and the poor solvent at a constant speed, and the fluorine resin solution and the poor solvent may be mixed in the outer tube to be granulated. Further, the fluorine resin solution may be passed through the outer tube and the poor solvent into the inner tube.

For example, in a T-shaped pipe, a poor solvent may be passed through from a direction of 90 degrees with respect to the flow of the fluororesin solution so that the fluororesin solution and the poor solvent are brought into contact with each other to be granulated.

The method of PFR is not limited to the above, since various kinds of piping can be used to mix the fluororesin solution and the poor solvent so as to be continuously granulated.

When PFR is used, the passing speed of the fluororesin solution and the passing speed of the poor solvent are not particularly limited as long as they can generate the fluororesin particles. From the viewpoint of productivity, the ratio of the flow rate of the fluororesin solution to the flow rate of the poor solvent is preferably 0.1 to 100, more preferably 0.2 to 50.

In addition, the mixing portion of the fluororesin solution and the poor solvent may be a pipe only, or a tubular mixing device may be provided. And a tubular mixing device in which a static mixing structure such as the mixing device or static mixer is stored as a tubular mixing device.

The mixing time of the fluororesin solution and the poor solvent may be within the same range as the residence time. The inner diameter of the pipe is not particularly limited as long as the fluororesin solution and the poor solvent are mixed. From the viewpoint of productivity, 0.1 mm to 1 m is preferable, and 1 mm to 1 m is more preferable.

When two pipes are used as the inner pipe and the outer pipe, the ratio of the inner pipe diameter to the outer pipe diameter is not particularly limited as long as the granulated liquid can be used. An outer diameter / inner diameter = 1.1 to 500, more preferably an outer diameter / inner diameter = 1.1 to 100.

Examples of the poor solvent for the fluororesin particles include aliphatic hydrocarbon solvents such as pentane, hexane, heptane, octane, nonane and decane, aromatic hydrocarbon solvents such as benzene, toluene, o- Ester solvents such as ethyl acetate, methyl acetate, butyl acetate and butyl propionate; ether solvents such as diethyl ether, diisopropyl ether, tetrahydrofuran and dioxane; alcohols such as methanol, ethanol, 1-propanol, Based solvent, water, and the like.

Preferably an alcohol solvent such as methanol, ethanol, 1-propanol or 2-propanol, or water. Particularly preferred are methanol, ethanol and water.

From the viewpoint of uniformly dispersing the fluororesin particles in the poor solvent, the poor solvent of the fluororesin is preferably a solvent which is uniformly mixed with the solvent used for the dissolution. Here, "uniformly mixed with each other" means that the interface is not exposed even if mixed with two or more solvents and allowed to stand for one day. For example, water can be used as a solvent in which NMP, DMF, DMAc, acetone, DMSO, tetrahydrofuran, acetonitrile, methanol, ethanol and the like are uniformly mixed with each other.

The poor solvent of the fluororesin may be a single solvent or a mixture of two or more solvents as long as it is mixed with the solvent used for dissolution. It is preferable to use a mixed solvent containing water, such as a water-alcohol or a water-nitrile mixed solvent, in view of the fact that fine particles having uniform particle diameters are easily obtained.

The amount of the poor solvent of the fluororesin to be used is not particularly limited and may be from 0.1 part by mass to 100 parts by mass with respect to 1 part by mass of the solvent used for dissolution. Preferably 0.1 part by mass or more and 50 parts by mass or less, and more preferably 0.1 parts by mass or more and 10 parts by mass or less.

When the fluororesin solution is added to the poor solvent of the fluororesin, the temperature of the bath may be set at 0 ° C or higher and lower than the boiling point of the poor solvent. Depending on the solvent to be used, there is a case where the particles are not fused due to fusion between the particles, and therefore it is preferable that the temperature of the receiving tank immediately before the addition is 0 deg. C or more and 40 deg. C or less. By this addition, the fluororesin particles are precipitated from the fluororesin solution, and a liquid or suspended liquid in which the fluororesin particles are dispersed is obtained. Further, when the fluororesin solution is added, it is preferable to stir the poor solvent of the fluororesin.

(a2 step), the dissolved fluorine resin solution is flash-crystallized to precipitate the fluorine resin particles. That is, in the method of adding the fluororesin solution to the poor solvent, the flash crystallization method is used. Flash crystallization is a method of rapidly solidifying and crystallizing a fluororesin solution. More concretely, it is preferable to use a fluororesin solution under a heating / pressurizing condition in which the solvent used for the dissolution is less than the boiling point (at or below room temperature) of the solvent at normal pressure and the pressure of the fluororesin solution is less than the pressure (Hereafter also referred to as a receiving tank) through a nozzle, deliming and crystallizing the fluororesin solution under pressure, or a method in which the fluororesin solution under pressure is mixed with another container (hereinafter referred to as " (Which may also be referred to as " receiving chamber ").

When the flash crystallization is carried out, it is preferable to directly spray the fluororesin solution into the poor solvent. It is preferable to perform flash crystallization while the tip of the nozzle from which the fluororesin solution is ejected is placed in a poor solvent on the receiving side. The tip of the nozzle may be separated from the poor solvent, and flash crystallization may be performed from above the poor solvent via the gas phase.

This will be described in detail. It is preferable to perform flash crystallization by ejecting the fluororesin solution from a container kept under heating, pressurization or pressurization toward a receiving tank under atmospheric pressure (the pressure may be increased). For example, in the above-mentioned dissolution step, when heated and dissolved in a pressure vessel such as an autoclave, the inside of the vessel is pressurized by the self-pressure by heating (it may be further pressurized with an inert gas such as nitrogen). And releasing it from the above state into the receiving tank under atmospheric pressure, so that it can be further simplified. In addition, when dissolved at room temperature, the fluorine resin particles can be obtained by pressurizing the dissolution tank at a certain pressure and flash-crystallizing toward a poor solvent of the fluorine resin.

The poor solvent to be used in the flash crystallization in the poor solvent is not particularly limited and the same solvent as that described in the step (a1) can be used.

The amount of the poor solvent of the fluororesin to be used is not particularly limited and may be in the range of 0.1 part by mass or more and 100 parts by mass or less based on 1 part by mass of the solvent used for dissolution. Preferably 0.1 part by mass or more and 50 parts by mass or less. More preferably 0.1 part by mass or more and 10 parts by mass or less.

As the operating conditions at the time of flash crystallization, a solution, usually dissolved in a temperature range of room temperature to 200 deg. C, preferably room temperature to 100 deg. C, is flash floated in a first stage in a container under reduced pressure, Or a method of performing flash crystallization in a multi-stage container in a container having a lower pressure than the inside of the tank containing the solution. Specifically, for example, in the above dissolution step, when heated and dissolved in a pressure vessel such as an autoclave, the inside of the vessel is brought into a pressurized state by self-pressure (elevation of pressure by heating) caused by heating It may be further pressurized with an inert gas). The pressurized solution is flashed toward the atmospheric pressure receiving vessel containing the poor solvent of the fluororesin or is flashed toward the receiving vessel under reduced pressure. Further, in the case of dissolving in a pressure-resistant container such as an autoclave, when the solution is dissolved without heating, the solution which has been pressurized under a certain pressure and is brought into a pressurized state is flashed toward the atmospheric pressure receiving tank containing the poor solvent of the fluororesin, As shown in FIG. The pressure (gauge pressure) of the solution to be subjected to flash filtration is preferably 0.2 MPa or more and 4 MPa or less. It is preferable that the solution in this environment is subjected to flash crystallization toward a receiving tank under atmospheric pressure.

The temperature of the holding tank differs depending on the poor solvent of the fluororesin to be contained in the holding tank and is preferably 0 ° C to 50 ° C as a temperature immediately before flash crystallization when the poor solvent of the fluororesin does not solidify to 50 ° C, .

In the flash crystallization method, there is a method in which the outlet of the connecting tube from the melting tank is placed in the air of the receiving tank or in a poor solvent of the fluororesin, followed by flash crystallization. It is preferable to put the fluororesin particles into a poor solvent since finer fluororesin particles can be obtained.

The fluororesin particles obtained by the precipitation step (a1 step), particularly (a2 step), can be obtained in the form of a dispersion or a suspension. In addition, in the case of including granules (coarse particles) such as unhardened components of the charged fluororesin, they can be removed by filtration or the like.

By adopting the method of the present embodiment, it is possible to stably produce fine fluororesin particles having uniform particle size. By using the polyvinylidene fluoride resin particles comprising a fluororesin particle, in particular a copolymer of vinylidene fluoride and hexafluoropropylene, the wet adhesiveness can be improved without lowering the air permeability.

Examples of the phase separation method include a method of forming a fluororesin particle by dissolving a fluororesin in a solvent, emulsifying the fluororesin solution using a non-solvent or the like, and bringing the solution into contact with a poor solvent.

As the dry pulverization method, a method of pulverizing fluororesin particles by colliding with each other or a method of pulverizing by colliding with a metal wall can be mentioned.

Examples of the wet grinding method include a method in which beads such as zirconia are added to a dispersion medium in which fluorine resin particles are dispersed, and the mixture is pulverized by stirring the beads and the fluorine resin particles. The material and bead diameter of the beads can be used according to the shape and size of the target fluoropolymer particles.

As a spray dryer method, there is a method in which droplets are formed by spraying a solution in which a fluororesin is dissolved in a solvent from a nozzle, followed by drying to form particles. The solvent used in the spray dryer system is not particularly limited as long as the fluororesin is dissolved, but a solvent having a lower boiling point than the melting point of the fluororesin is preferable. Specific examples thereof include acetone, methyl ethyl ketone, methyl isobutyl ketone, methanol, , 1-propanol, 2-propanol, 1-butanol, ethyl acetate, propyl acetate, butyl acetate, tetrahydrofuran and cyclohexanone.

(Inorganic particles)

In order to improve the dimensional stability of the separator for a secondary battery, it is preferable that the porous layer contains inorganic particles. The dimensional stability required for the separator for a secondary battery is preferably within 10% of the thermal shrinkage at 130 deg. C for 1 hour. As the inorganic particles, for example, they are required to be electrically stable in a battery, have electric insulation, and have heat resistance.

Specific examples of the inorganic particles include inorganic oxide particles such as aluminum oxide, bainite, silica, titanium oxide, zirconium oxide, iron oxide and magnesium oxide, inorganic particles such as aluminum nitride and silicon nitride, calcium fluoride, barium fluoride and barium sulfate Poorly soluble ionic crystal particles, and magnesium hydroxide. These particles may be used singly or in combination of two or more.

The average particle diameter of the inorganic particles to be used is preferably 0.10 μm or more and 5.0 μm or less. More preferably not less than 0.20 mu m and not more than 3.0 mu m, and still more preferably not less than 0.30 mu m and not more than 1.0 mu m. When the thickness is smaller than 0.10 탆, the porous layer may become dense, which may increase the degree of air permeability. In addition, since the hollow diameter is reduced, the impregnation property of the electrolytic solution is lowered, which may affect the productivity. If it is larger than 5.0 탆, sufficient dimensional stability may not be obtained, and the thickness of the porous layer may increase, which may lead to deterioration of battery characteristics.

Examples of the shape of particles to be used include a spherical shape, a plate shape, a needle shape, a bar shape, an oval shape and the like, and any shape may be used. Among them, spherical particles are preferred from the viewpoints of surface water repellency, dispersibility, and coating properties.

(bookbinder)

Wherein the fluororesin, the organic resin, the organic resin, the organic resin, the fluororesin and the inorganic particles, the organic resin and the inorganic particles, and the fluororesin, the organic resin, A binder may be used if necessary for binding each of the inorganic particles and the porous substrate. Further, by adding a binder, wet adhesion with the electrode, dry adhesion with the electrode, and dimensional stability may be improved.

Examples of the resin used for the binder include fluorine resin, acrylic resin, styrene-butadiene resin, crosslinked polystyrene, methyl methacrylate-styrene copolymer, polyamide, polyamideimide, polyimide, melamine resin, phenol resin, polyacrylonitrile , A silicone resin, a polycarbonate, and a carboxymethyl cellulose resin. These resins may be used singly or in combination of two or more. Of these binder resins, fluororesins, acrylic resins, styrene-butadiene resins, and carboxymethylcellulose are preferably used from the viewpoints of electrical stability and oxidation resistance, and fluororesins and acrylic resins are particularly preferable.

For the purpose of improving the dimensional stability, it is also possible to use polyamide, polyamideimide, polyimide, polyetherimide, polyvinylidene fluoride, vinylidene fluoride-hexafluoropropylene copolymer, polytetrafluoroethylene, polysulfone, polyketone , Polyether ketone, polycarbonate, polyacetal, and the like may be added. Herein, the heat-resistant resin means a resin having a melting point of 150 ° C or higher, or a resin having substantially no melting point. A resin having a melting point of 150 DEG C or higher is a resin having the peak top at 150 DEG C or higher. A resin having no melting point means a resin having no peak top at a measurement temperature range of -20 to 230 占 폚.

The binder to be used may be either a binder dissolved in a solvent or a particle-shaped binder, and the shape thereof is not particularly limited.

As the binder in the form of a particle, a part or all of the binder may be a coarse film at the time of forming the porous layer, or a coarse film may be used. As a method of forming the binder in the form of particles, there can be used a method of forming a binder by drying a film formed by heat at the time of drying the solvent or a method of forming a binder by using a solvent such as N-methyl-2-pyrrolidone, dimethylacetamide, dipropylene glycol methyl ether, butyl glycol, , 4-trimethyl-1,3-pentanediol monoisobutyrate, or the like may be added.

The average particle diameter of the binder in the particle form is preferably 1 占 퐉 or less. If it is larger than 1 mu m, the amount of the binder necessary for binding increases, which may deteriorate the battery performance.

The content of the binder is preferably 0.1 parts by mass or more and 100 parts by mass or less, more preferably 0.2 parts by mass or more based on 100 parts by mass of the total amount of the fluororesin, the organic resin, and the inorganic particles. More preferably 50 parts by mass or less, still more preferably 30 parts by mass or less. When the content of the binder is larger than 100 parts by mass, the content of the fluororesin and the organic resin becomes small, the contact area with the electrode becomes small, and the wet adhesion property and the dry adhesion property sometimes become weak. In addition, the increase in the air permeability is also increased, and the battery characteristics may be deteriorated. When the content of the binder is less than 0.1 part by mass, it is difficult to exhibit binding properties, so that the fluororesin and the inorganic particles laminated on the porous substrate are lost, making it difficult to form the porous layer.

(Formation of Porous Layer)

A separator for a secondary battery according to the present invention is a separator in which a porous layer composed mainly of inorganic particles and two or more kinds of organic resins having different melting points is laminated on at least one surface of a porous substrate, (A) and / or (B) of the separator according to the present invention. The method will be described below.

(A) the porous layer has a melting point of 130 ° C or more and 20 ° C or more and less than 130 ° C

(B) The porous layer has a melting point of 130 ° C or higher and has an amorphous organic resin.

The coating liquid is prepared by dispersing a fluororesin prepared by a known production method such as emulsion polymerization, suspension polymerization, dispersion polymerization, or the like, or a fluororesin and an inorganic particle processed to an intended average particle size and shape after polymerization. Here, as the solvent to be dispersed, a solvent containing water as a main component is preferable in that impregnation of the solvent into the porous substrate is suppressed. Here, the main component means that at least 50 mass% of the solvent is contained in 100 mass% of the solvent.

The proportion of water in the solvent containing the water as a main component is preferably 50 mass% or more, more preferably 60 mass% or more, and further preferably 70 mass% or more. When the proportion of water is less than 50% by mass, there is a case that a desired porous layer can not be formed by impregnating the substrate with the coating liquid when it is applied to the porous substrate. Further, when the coating liquid is impregnated, the conveying of the porous substrate becomes difficult, and wrinkles may occur during transportation.

When the fluororesin, the organic resin and the inorganic particles are dispersed, a dispersant may be used if necessary. Examples of the dispersing agent include, but are not limited to, cationic surfactants such as alkylamine salts and quaternary ammonium salts, alkylsulfuric acid ester salts, polyoxyethylene alkyl ether sulfuric acid ester salts, alkylbenzenesulfonic acid salts and fatty acid salts Nonionic surfactants such as anionic surfactants, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenols, glycerin fatty acid esters and polyoxyethylene fatty acid esters; amphoteric surfactants such as alkyl betaines and alkylamine oxides; Based surfactant, an anionic surfactant, a nonionic surfactant, a positive fluorinated surfactant, and a silicone surfactant. In addition, polymer compounds such as polyvinyl pyrrolidone, polycarboxylic acid salts, polysulfonic acid salts and polyethers can be given. These dispersants may be used singly or in combination of two or more.

The addition amount of the dispersing agent is preferably 0.1 parts by mass or more and 40 parts by mass or less, more preferably 0.2 parts by mass or more, and even more preferably 0.5 parts by mass or less, based on 100 parts by mass of the total amount of the fluororesin, organic resin, Or more. Further preferably not more than 30 parts by mass, more preferably not more than 20 parts by mass. If the addition amount of the dispersing agent is more than 40 parts by mass, the content of the fluororesin in the porous layer becomes small, so that the wet adhesion property and the dry adhesion property may be lowered.

As a method for dispersing the fluororesin, the organic resin, and the inorganic particles, a known method may be used. A ball mill, a bead mill, a sand mill, a roll mill, a homogenizer, an ultrasonic homogenizer, a high-pressure homogenizer, an ultrasonic device, and a paint shaker. The plurality of mixed dispersing units may be combined to perform the dispersion stepwise.

The order of preparing the coating liquid is not particularly limited. From the viewpoint of efficiency of the dispersion process, it is preferable to add and disperse a dispersing agent in a solvent containing water as a main component and add a fluororesin, an organic resin and inorganic particles to the solution to prepare a coating liquid.

The binder may be added to the coating liquid, if necessary, in order to bond the particles and the porous substrate together. If necessary, antioxidants, stabilizers, antifoaming agents, leveling agents and the like may be added to the coating liquid as appropriate.

Examples of the leveling agent include, but are not limited to, cationic surfactants such as alkylamine salts and quaternary ammonium salts, alkylsulfuric acid ester salts, polyoxyethylene alkyl ether sulfuric acid ester salts, alkylbenzenesulfonic acid salts, Nonionic surfactants such as polyoxyethylene alkyl ethers, polyoxyethylene alkylphenols, glycerin fatty acid esters and polyoxyethylene fatty acid esters; amphoteric surfactants such as alkyl betaines and alkylamine oxides; A cationic surfactant, an anionic surfactant, a nonionic surfactant, a positive fluorinated surfactant, a silicone surfactant, and a polymer compound such as polyvinylpyrrolidone, polycarboxylate, polysulfonate, and polyether.

The amount of the leveling agent to be added is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less based on 100 parts by mass of the total amount of the fluororesin, organic resin and inorganic particles. If the amount of the leveling agent added is more than 20 parts by mass, the adhesion may be deteriorated and battery characteristics may be deteriorated due to side reactions in the secondary battery.

Next, the coating liquid thus obtained is coated on the porous substrate and dried to laminate the porous layer. As a coating method, it may be applied by a known method. For example, gravure coating, slit die coating, knife coating, kiss coating, roll coating, bar coating, spray coating, dip coating, spin coating, screen printing, ink jet printing, putting printing and other kinds of printing can be used. The coating method is not limited thereto but may be selected in accordance with the preferable conditions of the fluororesin, organic resin, inorganic particle, binder, dispersing agent, leveling agent, solvent and substrate to be used. Further, in order to improve the coating property, for example, surface treatment of a coated surface such as corona treatment or plasma treatment may be performed on the porous substrate.

When the porous layer is laminated on both surfaces of the porous substrate, it may be applied one by one and dried. It is preferable to coat and dry both surfaces at the same time because productivity is good.

From the viewpoints of wet adhesion and dry adhesiveness, it is preferable that the porous layer is laminated on both sides of the porous layer only on one side, since wet adhesion and dry adhesion are both obtained on the positive electrode and the negative electrode, desirable.

The proportion of the organic resin having a melting point of 130 ° C or higher in the porous layer is preferably 1% by mass or more and 90% by mass or less, more preferably 5% by mass or more, and further preferably 70% % Or less. More preferably not less than 10% by mass, and not more than 50% by mass. When the proportion of the fluororesin in the porous layer is less than 1% by mass, sufficient wet adhesion may not be obtained. On the other hand, when the content is larger than 90% by mass, the content of the inorganic particles is lowered, so that sufficient dimensional stability may not be obtained.

The proportion of the organic resin having a melting point in the porous layer of 20 占 폚 or more and less than 130 占 폚 is preferably 1% by mass or more and 90% by mass or less, more preferably 5% by mass or more, Or less and 70 mass% or less. More preferably not less than 10% by mass, and not more than 50% by mass. When the proportion of the organic resin having a melting point in the porous layer of 20 占 폚 or more and less than 130 占 폚 is less than 1% by mass, sufficient dry adhesiveness may not be obtained. On the other hand, when the content is larger than 90% by mass, the content of the inorganic particles is lowered, so that sufficient dimensional stability may not be obtained.

The fluororesin and the organic resin may have the same constitutional unit, for example, a constituent unit in which the fluororesin and the organic resin are mixed in the same particle, respectively, for example, a fluororesin particle and an organic resin particle, The organic resin film is preferable from the viewpoint of wet adhesion with electrodes and dry adhesiveness.

The thickness of the porous layer is preferably 0.10 μm or more and 5.0 μm or less. More preferably not less than 0.3 mu m, and further not more than 4.0 mu m. More preferably not less than 0.5 mu m, and further not more than 3.0 mu m. When the thickness of the porous layer is thinner than 0.10 占 퐉, sufficient wet adhesion and dry adhesion with the electrode may not be obtained. When the thickness is larger than 5.0 占 퐉, the increase of the air permeability may increase, or the wet adhesion and the dry adhesion may become insufficient. In addition, when laminated only on one side, the curl may become remarkable, so it is preferable to laminate the porous layer on both surfaces of the porous substrate. In the case of laminating on both sides for the same reason, it is preferable that the difference in thickness of the porous layer on each surface is 1 占 퐉 or less.

It is preferable that the increase in air permeability due to the lamination of the porous layer is 5 times or less. More preferably 3 times or less. If the air permeability is increased by more than 5 times by the lamination of the porous layers, the total degree of permeability as a separator for a secondary battery becomes large, sufficient ion mobility can not be obtained, and battery characteristics may be deteriorated.

[Porous substrate]

In the present invention, examples of the porous substrate include a porous membrane sheet having a hollow therein, a nonwoven fabric, or a porous membrane sheet made of a fibrous material. The material constituting the porous substrate is preferably composed of a resin which is electrically insulative, electrically stable, and stable to an electrolytic solution. A resin to be used from the viewpoint of giving a shutdown function is preferably a thermoplastic resin having a melting point of 200 캜 or lower. The shutdown function herein is a function of stopping generation of electricity by stopping ion movement by closing the porous structure by melting with heat when the lithium ion battery abnormally generates heat.

As the thermoplastic resin, for example, a polyolefin resin can be mentioned, and the porous substrate is preferably a polyolefin porous substrate. It is more preferable that the polyolefin porous substrate is a polyolefin porous substrate having a melting point of 200 ° C or lower. Specific examples of the polyolefin resin include polyethylene, polypropylene, a copolymer thereof, and a mixture thereof. Examples of the polyolefin resin include a single-layer porous substrate containing 90 mass% or more of polyethylene, a multilayered structure of polyethylene and polypropylene And the like.

Examples of the production method of the porous substrate include a method of making the polyolefin resin into a sheet and then making it porous by stretching, and a method of making the sheet into a sheet by dissolving the polyolefin resin in a solvent such as liquid paraffin and then extracting the solvent to make it porous.

The thickness of the porous substrate is preferably from 5 占 퐉 to 50 占 퐉, and more preferably from 5 占 퐉 to 30 占 퐉. If the thickness of the porous substrate is larger than 50 占 퐉, the internal resistance of the porous substrate may be increased. If the thickness of the porous substrate is smaller than 5 占 퐉, the production becomes difficult and sufficient mechanical properties may not be obtained.

The air permeability of the porous substrate is preferably 50 sec / 100 cc or more and 1,000 sec / 100 cc or less. More preferably 50 sec / 100 cc or more and 500 sec / 100 cc or less. If the air permeability is higher than 1,000 sec / 100cc, sufficient ion mobility can not be obtained and battery characteristics may be deteriorated. If it is smaller than 50 sec / 100cc, sufficient mechanical properties may not be obtained.

[Separator for secondary battery]

As described above, the separator for a secondary battery according to the present invention is a separator in which at least one surface of a porous substrate is formed by laminating inorganic particles and a porous layer containing two or more kinds of organic resins having different melting points as main components, , And satisfies the following (A) and / or (B).

(A) the porous layer has a melting point of 130 ° C or more and 20 ° C or more and less than 130 ° C

(B) The porous layer has a melting point of 130 ° C or higher and has an amorphous organic resin.

It is preferable that the laminated porous layer is sufficiently polished to have ion permeability, and it is preferable that the permeability of the separator for a secondary battery is 50 sec / 100 cc or more and 1,000 sec / 100 cc or less. More preferably 50 sec / 100 cc or more and 500 sec / 100 cc or less. If the air permeability is higher than 1,000 sec / 100cc, sufficient ion mobility can not be obtained and battery characteristics may be deteriorated. If it is smaller than 50 sec / 100cc, sufficient mechanical properties may not be obtained.

[Secondary Battery]

The separator for a secondary battery of the present invention can be suitably used for a secondary battery such as a lithium ion battery. The lithium ion battery has a structure in which a separator for a secondary battery and an electrolyte are interposed between a positive electrode in which a positive electrode active material is laminated on a positive electrode collector and a negative electrode in which a negative electrode active material is laminated on a negative electrode collector.

The positive electrode is, the active material, a binder resin, and a positive electrode made of a conductive additive material will deposited on the collector, the active material as _{LiCoO 2, LiNiO 2, Li (} NiCoMn) O 2, a lithium-containing transition metal oxide of a layered structure, such as, LiMn ₂ O ₄ , and iron-based compounds such as LiFePO ₄ . As the binder resin, a resin having high oxidation resistance may be used. Specific examples include fluororesins, acrylic resins, and styrene-butadiene resins. As the conductive additive, carbon materials such as carbon black and graphite are used. As the current collector, a metal foil is suitable, and aluminum is often used.

As the active material, a carbon material such as artificial graphite, natural graphite, hard carbon, and soft carbon, a lithium alloy material such as tin or silicon, a metal such as Li, or the like is used as the negative electrode material comprising the active material and the binder resin. And lithium titanate (Li ₄ Ti ₅ O ₁₂ ). As the binder resin, a fluororesin, an acrylic resin, a styrene-butadiene resin or the like is used. As the current collector, a metal foil is suitable, and a copper foil is often used.

The electrolyte is a field for moving ions between a positive electrode and a negative electrode in a secondary battery, and the electrolyte is dissolved in an organic solvent. As the electrolyte, LiPF ₆ , LiBF ₄ , LiClO ₄ and the like can be mentioned, but LiPF ₆ is suitably used from the viewpoints of solubility in an organic solvent and ionic conductivity. Examples of the organic solvent include ethylene carbonate, propylene carbonate, fluoroethylene carbonate, dimethyl carbonate, diethyl carbonate, ethylmethyl carbonate, gamma-butylolactone and sulfolane, and two or more kinds of these organic solvents may be mixed May be used.

As a manufacturing method of the secondary battery, first, a positive electrode and a negative electrode are obtained by dispersing an active material and a conductive auxiliary agent in a binder solution to prepare a coating solution for electrode, applying the coating solution onto a current collector, and drying the solvent. The film thickness of the coated film after drying is preferably 50 占 퐉 or more and 500 占 퐉 or less. A separator for a secondary battery is disposed between the obtained positive electrode and negative electrode so as to be in contact with the active material layer of each electrode, sealed in a casing such as an aluminum laminate film, and then an electrolytic solution is injected and then hot pressed. After that, a negative electrode lead or a safety valve is installed, and the casing is sealed. The secondary battery thus obtained is excellent in cycle property, dimensional stability, and low cost because of good adhesion between the electrode and the separator for a secondary battery.

Example

Hereinafter, the present invention will be described concretely with reference to Examples, but the present invention is not limited thereto at all. The measurement method used in this embodiment is shown below.

[How to measure]

(1) Melting point

In the differential scanning calorimetry (DSC) according to "JIS K7121: Method of measuring transition temperature of plastic 2012", 6 to 7 mg of resin or porous layer was put into a measuring pan with a differential scanning calorimeter (DSC) manufactured by PerkinElmer Measurement was made under the following conditions. The temperature of the peak top of the endothermic peak at the time of the second temperature rise after the first temperature rise and cooling was taken as the melting point.

Temperature rise and cooling rate: ± 10 ° C / min

Measuring temperature range: -20 ~ 230 ℃.

(2) average particle diameter

The surface of the porous layer was observed at a magnification of 50,000 times using an electrolytic radial scanning electron microscope (S-3400N manufactured by Hitachi, Ltd.). The image size at that time is 2.5 占 퐉 占 1.8 占 퐉. The number of pixels was 1,280 pixels x 960 pixels, and the size of one pixel was 2.0 nm x 1.9 nm.

With regard to the average particle diameter, a square or a rectangle having the smallest area completely enclosing one particle is obtained on the obtained image, that is, a quadrangle or a rectangle in which the ends of the particle are in contact with the four sides of a square or a rectangle, (Long axis diameter) in the case of a rectangular shape as the particle diameter. The particle diameter of each 100 particles was measured, and the number average value was taken as the average particle diameter. When 100 or more particles are observed in the photographed image, the number average of any 100 particle diameters in the image is taken as an average particle diameter. When 100 particles are not observed in the image, a plurality of images are photographed And the number average of a total of 100 particle diameters was defined as an average particle diameter.

(3) Weight average molecular weight

The weight average molecular weight of the fluororesin was calculated by using a gel permeation chromatography method in comparison with a calibration curve by polystyrene.

Device: Seishin Shimazu Corporation LC-10A Series

Column: KD-806M x 2 manufactured by Showa Denko K.K.

Mobile phase: Dimethylformamide

Flow rate: 1.0 ml / min

Detection: differential refractometer

Column temperature: 40 占 폚.

(4) Thickness of the porous layer

The cross section of the sample was cut out with a microtome and the cross section was observed with an Electron Radiation Scanning Electron Microscope (S-3400N manufactured by Hitachi, Ltd.). The highest point was selected from the interface with the porous substrate in the observation region, As a film thickness. Each sample was observed, selected, and measured at five arbitrary positions from a sample of a size of 100 mm x 100 mm, and the average was averaged.

(5) Specularity

One arbitrary point was selected from three samples each having a size of 100 mm x 100 mm, and the measurement was carried out in accordance with JIS P 8117 (2009) using an Oken type air permeability measuring apparatus (EG01-5-1MR manufactured by Asahi Denka Co., Ltd.) And the average value thereof was determined as the air permeability (sec / 100cc).

(6) Wet bond strength

A solvent mixture of diethyl carbonate and ethylene carbonate in a mass ratio of 7: 3 was prepared. A 15 mm x 100 mm separator film for a secondary battery prepared in the following example, LiCoO _{2 as an} active material, a vinylidene fluoride resin as a binder, The conductive auxiliary agent was set so that the active material and the porous layer were brought into contact with each other after immersing the positive electrode 15 mm x 100 mm of the carbon black for 10 minutes and then taken out and subjected to hot pressing at 0.5 MPa and 100 캜 for 2 minutes using a hot press machine, Peeling was carried out manually, and wet adhesion strength was evaluated in four steps. Likewise, the wet adhesion strength of the graphite as the active material, the vinylidene fluoride resin as the binder, and the negative electrode of the carbon black as the binder and the separator for the secondary battery were measured, and each of the positive electrode and the negative electrode was evaluated.

Wet bond strength S: The electrode and the separator for the secondary battery were peeled off with a strong force.

Wet bond strength A: The electrode and the separator for the secondary battery were peeled off with a slightly strong force

Wet bonding strength B: The electrode and the separator for the secondary battery were peeled off with a weak force

Wet bond strength C: The electrode and the separator for the secondary battery were peeled off with an extremely weak force.

(7) Dry bond strength

The active material was LiCoO ₂ , the binder was a vinylidene fluoride resin, and the conductive auxiliary was a carbon black positive electrode 15 mm x 100 mm and a separator for a secondary battery. The active material and the porous layer were brought into contact with each other. / Min, and peeling was performed manually using tweezers, and the dry adhesion strength was evaluated in four steps. Likewise, the dry adhesion strength of the graphite as the active material, the vinylidene fluoride resin as the binder, and the negative electrode of the carbon black as well as the separator for the secondary battery were measured, and the positive electrode and the negative electrode were each evaluated to obtain the dry adhesion strength.

Dry bond strength S: The electrode and the separator for the secondary battery were peeled off with a strong force

Dry adhesive strength A: The electrode and the separator for the secondary battery were peeled off with a slightly strong force

Dry bond strength B: The electrode and the separator for the secondary battery were peeled off with a weak force

Dry bond strength C: The electrode and the separator for the secondary battery were peeled off with an extremely weak force.

(8) Heat shrinkage (dimensional stability)

The length of the midpoint of the feces was measured from the midpoint of one side of a sample of 100 mm x 100 mm size, and heat treatment was carried out in an oven at 130 캜 for 1 hour under an emulsion force. After the heat treatment, the sample was taken out, and the length between the middle points at the same point before the heat treatment was measured, and the heat shrinkage ratio was calculated from the following equation. Two samples were sampled from one sample at the same time, and the average value was determined as a heat shrinkage.

Heat shrinkage ratio (%) = [(length between middle points before heat treatment - length between middle points after heat treatment) / (length between middle points before heat treatment)] x100.

(Example 1)

(Polyvinylidene fluoride resin, vinylidene fluoride content: 95 mol%, containing carboxylic acid group as an acidic functional group, melting point: 160 DEG C) composed of a copolymer of vinylidene fluoride and hexafluoropropylene was mixed with the vinylidene fluoride and hexafluoro Was dissolved in 9,000 parts by mass of acetonitrile relative to 100 parts by mass of a copolymer of propylene with ethylene oxide at 80 DEG C and 11 parts by mass of water was added to 100 parts by mass of acetonitrile to prepare a polyvinylidene fluoride resin solution. The above polyvinylidene fluoride resin solution at 76 DEG C was continuously added to a tank of water (hereinafter referred to as a " granulation bath ") at a room temperature of 5,000 parts by mass with respect to 100 parts by mass of the copolymer of vinylidene fluoride and hexafluoropropylene , And a granulated liquid was obtained.

Then, 5,000 parts by mass of water (room temperature) relative to 100 parts by mass of the separately prepared polyvinylidene fluoride resin solution (76 ° C) was simultaneously dropped to the above-mentioned granulation bath at a rate of dropping for 6 minutes, To keep the liquid surface of the liquid, the granulating liquid was taken out from the bottom of the granulating bath (particle liquor A). Subsequently, while simultaneously dropping the polyvinylidene fluoride resin solution (76 ° C) separately adjusted and 5,000 parts by mass of water (room temperature) relative to 100 parts by mass of the copolymer at the rate of dropping for 6 minutes at the same time, The granulation liquid was taken out from the bottom of the granulation bath to keep the liquid level of the liquid (liquid for granulation B).

The granulating liquid A, the granulating liquid B, and the granulating liquid C remaining in the granulating tank were combined and the acetonitrile was distilled off under reduced pressure, and then the residue was centrifuged. 500 parts by mass of ion-exchanged water was added to 100 parts by mass of the obtained functional cake, and the slurry was washed and centrifugally filtered. 4 parts by mass of polyvinylpyrrolidone as a dispersing agent was added to 100 parts by mass of the fluororesin in the functional cake, ion-exchanged water was added so that the concentration of the fluororesin was 6 mass%, and the mixture was preliminarily dispersed by a homomixer. After the preliminary dispersion liquid was treated with ultrasonic waves (output: 120 W), the granulation was separated by centrifugal sedimentation to obtain an aqueous dispersion liquid of fluororesin particles having an average particle diameter of 0.10 m. The weight average molecular weight of the obtained fluororesin was measured to be 2.2 million.

Polyethylene (melting point: 80 占 폚) was used as the fluororesin aqueous dispersion, and aluminum oxide particles (average particle diameter: 0.50 占 퐉) as inorganic particles as non-volatile solid components , And 0.95 parts by mass based on 100 parts by mass of a total of 100 parts by mass of the fluororesin, the organic resin and the inorganic particles were added as the binder, and the perfluoroalkyl compound was added as the surfactant 0.7 parts by mass based on the total 100 parts by mass of the fluororesin and the aluminum oxide particles were added to prepare a coating liquid. This coating liquid was coated on both sides of a polyethylene porous substrate (thickness: 7 mu m, air permeability: 120 sec / 100 cc) by gravure coating and dried until the contained solvent volatilized to form a porous layer, .

The fluorine-containing resin has a melting point of the fluororesin, a weight average molecular weight of the fluororesin, an average particle diameter of the fluororesin particles, a vinylidene fluoride content of the fluororesin, a presence or absence of an acidic functional group of the fluororesin, (The ratio of the fluororesin in the table), the kind of the organic resin different from the fluororesin (hereinafter also referred to as "organic resin"), the melting point of the organic resin, the fluororesin, Table 1 shows the ratio of the organic resin in the total of the inorganic particles ("organic resin ratio" in the table). The proportion of the fluororesin was 19 mass%, and the proportion of the organic resin was 19 mass%.

The obtained secondary battery separator was measured for the thickness of the porous layer, the melting point of the porous layer, the air permeability, the wet bonding strength, the dry bonding strength and the heat shrinkage. The measurement results are shown in Table 2.

(Example 2)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 1 except that polyvinylidene fluoride (melting point: 90 占 폚) was used for the organic resin.

(Example 3)

Polyethylene (melting point 80 占 폚) and polyvinylidene fluoride (melting point 90 占 폚) were used in a mass ratio of 1: 4 to the organic resin and the proportion of the fluororesin in the total of the fluororesin, organic resin and inorganic particles was 19 Mass%, and the organic resin ratio was 23 mass%, the same procedure as in Example 1 was carried out to obtain the separator for a secondary battery of the present invention.

(Example 4)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 1 except that polypropylene (melting point: 100 占 폚) was used as the organic resin.

(Example 5)

Polypropylene (melting point 100 占 폚) and polyvinylidene fluoride (melting point 90 占 폚) were used in an amount of 1: 4 in the mass ratio so that the ratio of the fluororesin in the total of the fluororesin, organic resin, 19 mass%, and the organic resin ratio was 23 mass%, a separator for a secondary battery of the present invention was obtained in the same manner as in Example 1.

(Example 6)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 1 except that polyethylene (melting point: 120 占 폚) was used as the organic resin.

(Example 7)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 1 except that a fluororesin having a melting point of 130 占 폚 and a weight average molecular weight of 500,000 was used.

(Example 8)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 1 except that an acrylic resin (melting point 80 캜) was used as the organic resin.

(Example 9)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 1 except that a fluororesin having a melting point of 180 캜 was used.

(Example 10)

Same as Example 1 except that a resin (polyvinylidene fluoride resin, vinylidene fluoride content: 95 mol%, no acidic functional group, melting point: 160 ° C) consisting of a copolymer of vinylidene fluoride and hexafluoropropylene was used as the fluororesin Thereby obtaining the separator for a secondary battery of the present invention.

(Example 11)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 1 except that polyvinylidene fluoride (amorphous), which is an amorphous organic resin, was used for the organic resin.

(Example 12)

(Melting point 80 占 폚) and polyvinylidene fluoride (amorphous) which is an amorphous organic resin were used in an amount of 3: 2 by mass in the organic resin, and the amount of the fluororesin of the total of the fluororesin, , The ratio was 19 mass%, and the organic resin ratio was 23 mass%.

(Example 13)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 1 except that a fluororesin having a melting point of 190 占 폚, a weight average molecular weight of 2 million, and an average particle diameter of 0.25 占 퐉 was used.

(Example 14)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 1 except that the proportion of the fluororesin was changed to 10 mass%.

(Example 15)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 3 except that the proportion of the fluororesin was changed to 10 mass%.

(Example 16)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 14 except that the proportion of the fluororesin and the organic resin having a different melting point was changed to 5 mass%.

(Comparative Example 1)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 1 except that a fluororesin was not used.

(Comparative Example 2)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 1 except that the fluororesin had a melting point of 100 占 폚 and a weight average molecular weight of 40,000.

(Comparative Example 3)

A separator for a secondary battery of the present invention was obtained in the same manner as in Example 1 except that polyethylene (melting point: 150 占 폚) was used as the organic resin.

From Tables 1 and 2, it can be seen that Examples 1 to 10 and 13 to 16 of the present invention are separators in which porous layers composed mainly of two or more types of organic resins different in melting point from each other are laminated, (A) the porous layer has a melting point of not less than 130 ° C and not less than 20 ° C and not more than 130 ° C, so that good wet bond strength and dry bond strength to the electrode can be obtained and also low heat shrinkability ) Is obtained.

In Examples 11 and 12, a separator in which a porous layer mainly composed of two or more types of organic resins different in melting point from each other is laminated, wherein at least one kind of the organic resin is a fluororesin, and (B) ° C. or more and has an amorphous organic resin, a good wet bond strength and dry bond strength to the electrode can be obtained and a low heat shrinkability (high dimensional stability) can be obtained.

On the other hand, in Comparative Example 1, since the fluororesin is not contained, sufficient wet bonding strength with the electrode is not obtained. In Comparative Example 2, since the melting point of the fluororesin is low, sufficient wet bonding strength with the electrode can not be obtained. In Comparative Example 3, since the melting point of the organic resin is high, sufficient dry bonding strength with the electrode can not be obtained.

Claims (9)

A separator in which at least one surface of a porous substrate is formed by laminating an inorganic particle and a porous layer composed mainly of two or more kinds of organic resins having different melting points on a surface, wherein at least one of the organic resins is a fluororesin, and the following (A) and / B). ≪ / RTI >
(A) the porous layer has a melting point of 130 ° C or more and 20 ° C or more and less than 130 ° C
(B) the porous layer has a melting point of 130 ° C or higher and has an amorphous organic resin At least one kind of the organic resin is a fluororesin, and the porous layer has a thickness of not less than 130 占 폚 and not more than 20 占 폚. The separator is characterized in that at least one of the organic resin is a fluororesin, Lt; 0 > C to less than 130 < 0 > C. 3. The method according to claim 1 or 2,
A separator for a secondary battery, which satisfies (C) and / or (D) below.
(C) the porous layer has a melting point of 130 占 폚 or more and less than 180 占 폚 and 20 占 폚 or more and less than 130 占 폚
(D) the porous layer has a melting point of not less than 130 DEG C and less than 180 DEG C, and has an amorphous organic resin 4. The method according to any one of claims 1 to 3,
Wherein the organic resin comprises an acrylic resin and / or an olefin resin. 5. The method according to any one of claims 1 to 4,
Wherein at least one of the organic resins has an acidic functional group. 6. The method according to any one of claims 1 to 5,
Wherein the fluororesin is a polyvinylidene fluoride resin having a vinylidene fluoride content of 80 mol% or more and 100 mol% or less. The method according to claim 6,
Wherein the polyvinylidene fluoride resin has a melting point of 130 ° C or higher. 8. The method according to claim 6 or 7,
Wherein the polyvinylidene fluoride resin is in the form of particles and has an average particle diameter of at least 0.01 탆 and less than 1.00 탆. A secondary battery using the separator for a secondary battery according to any one of claims 1 to 8.